Cisco Catalyst 2960 Software Configuration Manual page 752

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Configuring QoS

Understanding QoS

SRR Shaping and Sharing

Both the ingress and egress queues are serviced by SRR, which controls the rate at which packets are

sent. On the ingress queues, SRR sends packets to the stack or internal ring. On the egress queues, SRR

sends packets to the egress port.

Catalyst 2960-S switches do not support ingress queueing.

You can configure SRR on egress queues for sharing or for shaping. However, for ingress queues, sharing

is the default mode, and it is the only mode supported.

In shaped mode, the egress queues are guaranteed a percentage of the bandwidth, and they are

rate-limited to that amount. Shaped traffic does not use more than the allocated bandwidth even if the

link is idle. Shaping provides a more even flow of traffic over time and reduces the peaks and valleys of

bursty traffic. With shaping, the absolute value of each weight is used to compute the bandwidth

available for the queues.

In shared mode, the queues share the bandwidth among them according to the configured weights. The

bandwidth is guaranteed at this level but not limited to it. For example, if a queue is empty and no longer

requires a share of the link, the remaining queues can expand into the unused bandwidth and share it

among them. With sharing, the ratio of the weights controls the frequency of dequeuing; the absolute

values are meaningless. Shaping and sharing is configured per interface. Each interface can be uniquely

For more information, see the

"Allocating Bandwidth Between the Ingress Queues" section on

"Configuring SRR Shaped Weights on Egress Queues" section on page

33-80, and the

"Configuring SRR Shared Weights on Egress Queues" section on page

Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE

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